Operation and control of water treatment chemical programs in industrial, municipal, or utility systems typically requires the monitoring of both physical and chemical performance indicators which are important to maintain process system protection. The physical and chemical performance indicators monitored typically include pH, specific anions and cations, inorganic and organic scale inhibitors, corrosion inhibitors, dispersants, and synthetic polymers, etc. It is key to the success of any treatment program that a minimum level, and sometimes a maximum level for economic reasons, of treatment chemicals be maintained in the system.
Control analyses of cooling water, boiler water, and wastewater systems, for example, still typically rely on grab samples. These samples are subsequently analyzed by conventional manual techniques with obvious shortcomings in time, economy and human-error possibilities. In fact, for most industrial water treatment processes analyses are historical rather than dynamic in nature.
Many industrial processes require constant surveillance and control especially process water systems. This requires rapid repetitive analysis with subsequent manual control adjustments or continuous automatic analysis with dynamic control adjustments wherein sensors are coupled directly to computer controllers which are capable of metering chemical feedpumps. A recent technique involves the use of metering devices driven by microprocessors which determine system demand (water flow). Another technique involves measuring an inert component which is added to the system in an amount which is proportional to the total product feed. Neither of the above methods provides a direct analysis of the active treating components and both of these methods assume that the concentration of active treating components are present in the system in a constant proportion which often is not the case. Both methods, therefore, require additional active treating component analyses to assure the correct level of inhibitor, etc.
Recently, ultra-violet, visible and near infrared detectors have been used to quantitatively analyze heavy metal contaminants in multi-component systems. Chemical analysis using ultraviolet, visible, near infrared absorption or emission spectra relies upon relative absorption or emission characteristics at many specific wavelengths over the entire ultraviolet and visible range. Absorption or emission in the ultraviolet, visible, and near infrared (UV-vis-NIR) region of the spectrum is a result of the changes in energy levels that occur in the bond structures and valence electrons of atoms when in contact with a source of ultraviolet-visible light.
The important features of absorption or emission spectra are its position and intensity, which yield a signature that can be used to define qualitative and quantitative characteristics. These data are a function of the absorption or emission intensities detected at many equally spaced wavelength intervals across a range of wavelengths. Absorption of light is governed by the Beer-Lambert Law that define the relationship between incident light absorbed by a solution and the molecular concentration of the solution. In simplified form, the Beer-Lambert law may be stated as: EQU A=abc
where,
A=The total amount of light absorbed. PA1 a=absorption coefficient defining PA1 b=length of the absorption light absorptivity of the media PA1 c=concentration of the solution PA1 T=transmittance PA1 A=absorbance PA1 I=intensity of absorbed light I.sub.0 PA1 I=intensity of incident light I.sub.0
Absorption may also be described in terms of a comparison between the intensity of light transmitted through an absorbing substance compared to the light intensity when no absorbing substance is in the light beam: EQU T=(I/I.sub.0) and, EQU A=log (1/T) or, EQU A=-log (.sub.0 /I)=abc
where,
It is possible to analyze solutions qualitatively and quantitatively based on the pattern of absorption or emission observed for the solution across this wide range of wavelengths. Since the observed absorption or emission is a function of all of the absorbing or emitting components within the solution, multi-component systems or systems having a high degree of background interferences greatly complicates the problem of analysis.
Several recent developments have made the use of ultraviolet-visible absorption or emission spectroscopy a feasible technology in the water treatment field:
fiber optics permit substantial distance between the analyzer and the substance to be analyzed. The remote analyzer can house a light source, detector, and electronic components. Fiber optic cables convey the source light to an optrode, where the light is transmitted through the sample, then collected and returned to the detector through a companion cable. Optrodes may be immersed in a process tank or flow stream, and then removed after the analysis has been performed, or they may be permanently located at the same point for continuous monitoring. These are two types of IN-SITU analysis. Alternatively, a sample line may be connected to a flow-through cell containing the optrode. This in ON-LINE analysis.
array detectors permit a broad wavelength range to be simultaneously detected at discrete intervals. This eliminates the need to create intervals by altering wavelengths at the source or prior to detection. Instead, a broad source can be used and fully detected. An evaluation can be made of wavelengths which contain absorption or emission features relevant for the analysis. Wavelengths and ranges which do not contain information that contribute to the analysis can be ignored, even though the measurement will include information from the entire range.
chemometrics may be the most meaningful advance in technology that makes on-line analysis possible. This technique is more fully explained in S. D. Brown, "Chemometrics", Anal. Chem. 62. 84R-101R (1990) which is incorporated herein by reference in its entirety.
Chemometrics is the application of statistical and pattern recognition techniques to chemical analysis. Quantitative estimates of chemical concentration in reagentless UV-vis-NIR spectroscopy are based on algorithms, the parameters of which are determined in calibration sequences called learning sets. Learning sets consist of a large number of known samples that are used to determine the parameters of the algorithm. The number of samples required depends on the complexity of the matrix and the number of spectroscopic interferences that are present. It also depends on the number of dependent variables used in the algorithm. As a rule of thumb, the number of samples should be at least 10 times the number of dependent variables employed. In the presence of known and unknown interferences, the goal of multiple sample calibration is to minimize out the effects of interferences. The learning set solutions must typify the interferences and their variability that will be experienced in on-line solutions measured by the analyzer.
Sensors that detect information for multiple constituents in a complex chemical matrix must rely upon very capable analysis algorithms (chemometric techniques) in order to extract information for a specific chemical constituent. These chemometric techniques compare unknowns with calibrated standards and data bases, to perform advanced forms of cluster analysis, and to extract features from unknowns that are used as information in statistical and mathematical models.
It is another object of this invention to provide a method for simultaneously analyzing multiple performance indicators in aqueous systems in real time.
It is another object of this invention to provide a method for simultaneously analyzing multiple performance indicators in aqueous systems without the use of derivitizing agents.
It is a feature of this invention that multiple performance indicators may be simultaneously analyzed in aqueous systems without the need to chromatographically separate the individual performance indicators or to separate background interferences.
It is another object of this invention to provide a method for maintaining an effective water treatment program wherein multiple performance indicators are directly and continuously monitored to detect change and provide control input to assure optimum dosage levels for some or all performance indicators in the aqueous system.
In accordance with the present invention, there has been provided a method for simultaneously measuring the concentration of multiple performance indicators in an aqueous system which comprises analyzing the ultra-violet, visible and/or near infrared spectrum of the aqueous system in the wavelength range of 200 to 800 nm and applying chemometrics algorithms to the spectrum to simultaneously determine the concentrations of the performance indicators.
Also provided in accordance with the present invention is a method for simultaneously measuring the concentrations of multiple performance indicators and one or more inert tracers in aqueous systems which comprises analyzing the ultra-violet, visible and/or near infrared spectrum of the aqueous system in the wavelength range of from 200 to 800 nm and applying chemometrics algorithms
Chemometric techniques have recently been found to be useful for the analysis of metals in aqueous media such as wastewater or contaminated groundwater where many different metals as well as other chemical constituents can be present, all of which may independently vary in concentration. Overlapping the closely grouped spectra from individual constituents result in a spectral signature for the solution that is a combination of individual elements. An analysis system must be capable not only of automatically detecting certain significant features for identification of the analytes of interest, it must also be capable of rapidly analyzing these features to arrive at qualitative identification of the analytes and quantitative measurements of their concentrations, and must do so in a chemical matrix that may contain many possible interferants in a variable background.
"On-site and On-line Spectroscopic Monitoring of Toxic Metal Ions using Fiber Optic Ultraviolet Absorption Spectroscopy" Schlager et al (1991) discloses the application of chemometrics for the analysis of heavy metals in water. "Environmental Monitoring using Chemometric Techniques with the Coming Generation of Smart Analyzers" Schlager et al (1991), discloses the application of chemometrics to the field of environmental monitoring. These references, which are incorporated herein their entirety, do not disclose simultaneous multiple analyses of performance indicators in aqueous systems.